Significant progress has been made in vehicular braking systems in recent years. Among these developments are different braking strategies such as anti-lock braking systems (ABS) and regenerative braking systems. The latter is used in electric and hybrid-electric vehicles. These braking strategies are interchangeably blended in order to brake a vehicle. Typically, a vehicle's brake pedal is mechanically decoupled from downstream braking circuits. A control valve typically regulates boost pressure from an accumulator to provide a regulated boost pressure to the downstream braking circuits. Since the brake pedal is mechanically decoupled, a brake pedal feel simulator is typically included in a braking system in order to provide a feedback to the operator of the vehicle.
In the event of a failure of the hydraulic system and/or the electrical regenerative system, it is necessary for the braking system to switch modes of operation so that the brake pedal is mechanically coupled to the downstream brake circuits. In such a failure mode, the force applied to the brake pedal is transferred to the downstream brake circuits to generate the necessary braking force to halt a vehicle.
There is a need to provide an improved braking system that is operable in a normal mode in which the brake pedal is mechanically decoupled from the downstream braking circuits and also operable in a failure mode in which the brake pedal is at least mechanically coupled to one downstream braking circuit.